Thin layers of length-sorted single wall carbon nanotubes (SWCNT), formed through filtration from a dispersing solvent onto a filter substrate ( buckypaper ), exhibit sharp changes in their optical and conductivity (s) properties with increasing SWCNT surface coverage. Longer tubes are found to be more transparent and conducting at the same coverage at optical frequencies and the IR absorption increases linearly with SWCNT concentration, regardless of SWCNT length. We show that changes of s with SWCNT concentration can be quantitatively described by generalized effective medium (GEM) theory. The scaling exponents describing the percolation transition from an insulating to conducting state with increasing concentration are consistent with two-dimensional percolation theory, provided that the SWCNTs are reasonably long. The conductivity percolation threshold xc was also found to vary with particle aspect ratio L as, xc ~ 1 / L, a result that also accords with the expectations of conductivity percolation theory. Our results provide a framework for engineering the properties of thin SWCNT layers for the numerous technological applications that are envisioned for buckypaper.
Citation: ACS Nano
Pub Type: Journals
carbon nanotubes, percolation theory, transparent conductive coatings,